(a) Field of the Invention
The invention relates to a display module for a hand-held device, and more particularly, to a display module for a mobile communication device being capable of reducing noise.
(b) Description of the Related Art
FIG. 1 shows an exploded view illustrating a conventional display for a mobile communication device. In the conventional display for mobile communication device 10, a display module is disposed in space defined by a lower casing 11 and an upper casing 12. The display module comprises a display panel 13, a driver 15 and a flexible printed circuit board (FPCB) 14. The display panel 13 is driven by an external driving voltage. To drive the display panel 13, a driver 15 is disposed on the display panel 13 and a FPCB 14 is coupled to the display panel 13. On the FPCB 14, a plurality of electronic components is disposed such as resistances, capacitors, etc. A speaker 17 is disposed on the upper casing 12 so that a user can hear the voice from another person during communication. When a mobile communication device is in operation, since the ear of the user is very close to the speaker 17, the user is very sensitive to the noise generated by the display for mobile communication device 10. In general, the manufacturer of mobile communication device will make a request that the noise generated by the display module for mobile communication device 10 should be conform to their noise measurement specification.
FIGS. 2A to 2B show a schematic diagram illustrating how a conventional display for mobile communication device generates noise. In operation of a conventional display for mobile communication device, a driving voltage applied into the display panel 13 is continuously varied to change the direction of the liquid crystal molecules. However, the dielectric medium in the capacitor 16 on the FPCB 14 is influenced by the continuously varied voltage differences, which results in swelling or shrinking of the capacitor 16. Furthermore, the surface of the FPCB 14 may have swelling or shrinking deformation due to the swelling or shrinking of the capacitor 16. As shown in FIG. 2B, the FPCB 14 vibrates with the swelling or shrinking of the capacitor 16 since the electric field caused by the voltage difference is varied with time. If the resonance due to vibration of the FPCB 14 has a frequency falling within the range that can be sensed by human being, noise occurs.
In one conventional technique, the characteristics of the capacitor 16 is altered to reduce the degree of deformation of the capacitor 16 influenced by the driving voltage. However, due to rising scrutiny of the display quality of a display module and gradually strict tolerance of noise, the effect of reducing noise by altering the characteristics of the capacitor 16 is already unable to satisfy practical application. FIGS. 3A to 3B show a schematic diagram illustrating how a conventional display for mobile communication device generates noise. As shown in FIGS. 3A to 3B, the capacitors 16 are symmetrically disposed on the top and bottom surfaces of the FPCB 14 so that the vibration of the FPCB 14 is reduced to decrease formation of noise. It is difficult, however, to dispose the capacitors 16 on the top and bottom surfaces of the FPCB 14 during manufacturing, and the thick of the FPCB 14 becomes thicker. As a result, it is not easy to dispose the FPCB 14 into the lower casing 11 and the upper casing 12, and then increasing the manufacturing complexity.